Attempt to resize the cache such that the total disk usage is under
the $new_size parameter. $new_size represents t size (in bytes)
that the cache should be limited to. Note that this is only a one
time adjustment. To maintain the cache size, consider using the
max_size option, although it is considered very expensive, and can
often be better achieved by peridocally calling limit_size.

If this property is set, then the cache will try not to exceed the max
size value (in bytes) specified. NOTE: This causes the size of the
cache to be checked on every set, and can be considered *very*
expensive in some implementations. A good alternative approach is
leave max_size as $NO_MAX_SIZE and to periodically limit the size of
the cache by calling the limit_size( $size ) method.